When you ask yourself how a harbor looked, then I think you should first focus on civilian traffic.
After all - allthough in war (or about to enter it) - life goes on.
So that means allot of regular ship-activities, concentrated on cargo and fishing.
Generally, you could expect any nationality.
The Navy is surely present - in the form of docked warships (resupplying/repair), and an occasional departure/arrival.
But the bulk of the traffic would be civilian.
Harbors were usually defended by mine-fields and subnets (obviously), and a couple of destroyers patrolling off the coast nearby.
Some stationary hydrophones may be present.
But most of the guarding would be done by units on the shore, in the form of lookouts, searchlights, and gun-positions.
After all, the most serious threat usually came from the sky (bombers), and not the sea.
Anyway, first line of defence wasn't really inside the harbor itself...it was formed by the recon-flights, extended patrols, and the radio-calls from units out at sea. These were the guys that were expected to report any abnormalies.
In August 1940, first experiments with short-wavelength radar were conducted, and soon the British coastlines (and harbors) would see the deployment of this equipment (which lead to the defeat of the Uboat-waffe anyway).
A Navy-base is something else, though...
